The present invention relates to means of monitoring and control of fuel combustion processes and, more precisely, to a method of determining heat losses due to incomplete fuel combustion and a device for implementing the same.
The invention is intended for use in systems of monitoring and control of fuel combustion processes at thermal power stations, in boiler plants and industrial furnaces, operating on solid, liquid and gaseous fuels.
The quality of fuel burning processes depends on the degree of completion of the combustion process in combustion chambers. The resultant heat losses are caused by chemical and mechanical underburning of fuel, and condition excessive consumption of the latter. The amount of these losses is dependent both on the construction of furnace and fuel burning preparation systems, and on the specifics of operation thereof. Control over the running values of these losses makes it possible to timely influence the operating conditions: supply of oxidizer (air), its temperature, and the degree of fuel comminution. Maintaining optimal values of these parameters allows heat losses due to incomplete fuel combustion and, consequently, excessive fuel consumption and discharge of unburnt fuel into the atmosphere to be reduced to a minimum. At the present time the problem of control over heat losses due to incomplete fuel combustion has not yet been fully solved. This is particularly true of operation on solid fuel, entailing considerable losses of heat due to both mechanical and chemical underburning. Control over mechanical underburning presents the most severe problem.
The value of heat losses caused by mechanical or chemical underburning is expressed in per cent of the amount of heat released in the event of complete fuel combustion and is calculated by relevant formulas, including calorific value of fuel, composition of combustible components remaining after burning thereof, heat of combustion, fuel ash content, and amount of ash in the fly ash and slag. These values vary considerably even within the same lot of fuel.
Monitoring of heat losses due to incomplete fuel combustion is generally carried out by analyzing the composition and the number of combustible components, the results of the analysis providing the basis for appraising the quality of the fuel combustion process. However, variability of values making part of the design formula is conducive the appreciable errors in determining heat losses due to incomplete fuel combustion, which does not alow the fuel combustion process to be optimized even in case of a very accurate analysis of combustible components in the remaining unburnt fuel.
One prior art method of determining chemical underburning of a liquid or a gaseous fuel (cf. USSR Inventor's Certificate No. 402,790, cl. F23 N 5/14) consists in that a sample of flue gases is separated into two parallel flows, with a dose of oxygen being injected in one of them, and a predetermined amount of a combustible component, in the other. The mixture is finish-burnt in each flow, and assessment is made of the amount of heat liberated thereat in each flow. The amount of combustibles in the sample is judged by the amount of heat released in the first flow, and the amount of oxygen contained in the sample is estimated on the basis of the amount of heat released in the second flow.
Separating the sample into two flows and introducing additional reagents complicates the method and conditions the dependence of the results of measurements on the precision of reagent metering, and omission of the running value of the fuel calorific power affects the accuracy in determining heat losses. Furthermore, heat loss estimation necessitates additional calculations. The method is not applicable to determining heat losses due to mechanical underburning.
Another prior art method of determining the content of combustibles in the fly ash (cf. USSR Inventor's Certificate No. 391,355, cl. F23 B 5/24) consists in that a sample of ash is passed between capacitor plates to measure the variation of its capacitance depending on carbon content in the sample.
Variation of carbon concentration gives rise to a change in the value of permittivity of the medium in the electric field of the capacitor. The results of measurements are largely influenced by the presence of other components making up the sample, and also by extraneous impurities. This circumstance causes insufficient accuracy of measuring the content of combustibles in the sample and the total error in determining heat losses due to incomplete fuel combustion.
Known in the art is a device for determining the content of combustibles in fly ash (cf. USSR Inventor's Certificate No. 375,449, cl. F23 N 5/24), comprising a sampler, a separator to isolate the coarse fraction of the sample, a screw feeder, a capacitor, and an indicator of carbon content in the sample.
Passsing the sample through the separator leaves particles of the fine fraction out of the sample, which does not give a clear idea of the sample composition and adds to the error in defining heat losses due to incomplete fuel combustion.
Another prior art method of determining heat losses due to incomplete fuel combustion consists in that a sample of fuel combustion products is periodically drawn, heated to the temperature of ignition of the combustible remaining in this sample to assist burning, and the quantity of heat given off after finish burning of the sample is assessed, whereby losses of heat due to incomplete fuel combustion are judged ("Power Stations" Journal, No. 1, 1973. K. N. Popov, E. V. Agafonov, L. N. Matonin. "Apparatus for Determining Heat Losses Due to Mechanical Underburning").
According to said method, the quantity of heat liberated during sample burning is determined from the change of temperature in the furnace, thereby estimating the amount of combustibles in the sample. Following this, appraisal is made of heat losses due to incomplete fuel combustion, taking into account ash content and fuel calorific value, additionally determined for calculations. The influence of errors in determining all values necessary for calculations reduces considerably the accuracy of assessing heat losses due to incomplete fuel combustion.
Also known in the art is a device for determining heat losses due to incomplete fuel combustion, comprising a chamber for finish burning of the sample, provided with an electric heater, and a means for measuring the thermal effect of the fuel combustion reaction associated with the chamber ("Power Stations" Journal, No. 1, 1973. K. N. Popov, E. V. Agafonov, L. N. Matonin. "Apparatus for Determining Heat Losses Due to Mechanical Underburning").
The chamber for finish burning of the sample incorporated in said device is made in the form of a cylinder with the axis thereof making an angle to the horizontal. The electric heater revolves around the chamber for finish burning of the sample. A sample of fuel combustion products is periodically charged into the chamber. As the chamber rotates, the sample is stirred and displaced along the axis of the chamber. The time of the sample finish burning is 10 minutes, which is sufficient for proximate laboratory analysis, but insufficient for timely interference in the process during automatic control of the fuel combustion process.
The thermal effect of the fuel combustion reaction is determined by a rise in temperature in the chamber for finish burning of the sample with the help of thermocouples installed therein. The amount of liberated heat is used to calculate the heat losses due to mechanical underburning of fuel.
Besides, fluidity of the heat flow during sample burning causes an appreciable error in measuring the temperature, whereby the content of combustibles in the sample is judged. The aforesaid does not allow precise and reliable assessment of heat losses due to incomplete fuel combustion.